In an optical reading system, for example, an optical pickup head is controlled in a radial direction to precisely follw any of a plurality of information tracks spirally formed on a rotatable disc in a normal playback mode and controlled in the same direction to move from one track position to another track position in an access mode. Such a syetem is disclosed in U.S. Pat. No. 4,397,009. In the U.S. Patent, a tracking zero signal of sinewave is detected in response to the radial movement of the pickup head relative to the rotatable disc and utilized to control the position of the pickup head. However, such a prior system is required to be separately provided with a positioning servo loop to control the pickup head so as to maintain the pickup head on an information track and a driving servo loop to move the pickup head to another position. Thus, it will be noted that the whole servo system is complicated and has many parts, which causes the servo system to be expensive.